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Heteroatom doping is widely recognized as an appealing strategy to break the capacitance limitation of carbonaceous materials toward sodium storage. However, the concrete effects, especially for heteroatomic phase transformation, during the sodium storage reaction remain a confusing topic. Here, a novel hypercrosslinked polymerization approach is demonstrated to fabricate pyrrole/thiophene hypercrosslinked microporous copolymer and further give porous carbonaceous materials with accurately regulated N/S dual doping corresponding to starting feeding ratios. Significantly, the N doping contributes to the conductivity and surface wettability, while the S doping is bridged to build stable active sites, which can be electrochemically converted into mercaptan anions via faraday reaction and further enhancing reversible capacities. Meanwhile, the abundant S doping can also conduce to the expanded interlayer spacing to shorten the ions diffusion distance, thus optimizing the reaction kinetic. As a result, the N0.2S0.8‐micro‐dominant porous carbon delivers the highest reversible capacity of 521 mAh g−1 at 100 mA g−1 and excellent cyclic stability over 2000 cycles at 2000 mA g−1 with a capacity decay of 0.0145 mAh g−1 per cycle. This work is anticipated to provide an in‐depth understanding of capacitance contribution and illuminate the heteroatomic phase transformation during sodium storage reactions for doping carbonaceous anodes.

In another example, intermetallics featuring smaller Pt [ , 8] Pd, [9] and Ir [10] atomic ensembles displayed higher formic acid oxidation reaction (FAOR) activity compared with corresponding monometallic nanoparticles. Thus, alloying is a feasible strategy to promote electrocatalytic performances. However, the random bimetallic alloy catalysts exhibit multiple types of atomic configurations, making it difficult to distinguish the most active coordination environment. In addition, the atomic utilization of noble metals, which usually working as the active sites, needs to be further promoted for common alloy catalysts.To achieve a full utilization of metallic atoms, single-atom catalysts (SACs) were developed in recent years. [11] Moreover, the significantly changed adsorption properties render SACs highly active in several reactions in which the metallic catalysts are inactive. For example, Fe, [12] Co, [13] Zn, [14] etc. SACs displayed superior ORR activity, enabling SACs promising cathodic catalysts in fuel cells. In the anodic reactions, Rh-N-C [15] and Ir-N-C [16] SACs exhibit ultrahigh FAOR activity surpassing state-ofthe-art Pd catalyst, while Rh and Ir nanoparticles are almost inert. Although SACs offer a full expose of metal sites, tuning the intrinsic activity is highly dependent on the substrates which anchored the single atomic sites. For instance, N-doped C anchored Pt SAC [16] displayed inferior FAOR performance while Au nanoparticles supported single atomic Pt [17] delivered excellent catalytic selectivity and activity, which may be attributed to the varying electronic structures of Pt. In view of the full utilization of active atoms in SACs and synergetic effects in alloys, combining their merits represents one of the most promising strategies to further promote electrocatalytic performance and acquiring structure-activity relationship in specific coordination environments. Thus, single-atom-alloys (SAAs), featuring with atomically dispersed metallic dopant atoms on the surface of metal hosts, [18] have been a kind of promising catalysts in heterogeneous catalysis. Commonly, the dopant atoms are active for specific reactions while the host metals are less reactive.The dopant element in SAA exhibits a free-atom-like electronic structure compared with host metal elements. [19] As shown in Figure 1a, the host metal Au exhibited the broad d-project density of states (DOS), while the dopant elements Pt and Ni exhibited the narrow d-project DOS, similar to the free-atom-like electronic states. Up to now, Pt-group metals are mainly employed as the dopants in SAAs to promote the Single-atom-alloys (SAAs), as an emerging kind of materials, combine the advantages of alloy and single-atom catalysts. The full atomic utilization of active sites and well-defined bonding environments in SAAs lead to superior electrocatalytic performance and give a deep insight into the structural-activity relationship. In this review, the recent advances of SAAs in various electrochemical reactions are highlighted for further...

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